1. Field of the Invention
The present invention relates to a cathode active material.
2. Description of the Related Art
Non-aqueous electrolyte rechargeable secondary batteries are conventionally used as secondary batteries for electric automobiles. The secondary batteries for automobiles are used in a high-current range during driving at high speed or climbing. Thus, it is desirable that the secondary batteries for automobiles, in addition to their high capacity, have excellent charge and discharge properties in a high-current range.
Metal fluorides represented by the general formula MF3 are known to be used as cathode active materials for the non-aqueous electrolyte secondary batteries. See Japanese Patent Laid-Open No. 2008-130265. M in the MF3 is a metal element selected from the group consisting of Fe, V, Ti, Co, and Mn.
The metal fluorides represented by the general formula MF3 are known to have a high theoretical energy density (reversible capacity). For example, a non-aqueous electrolyte secondary battery using FeF3 as a cathode active material and Li as an anode active material is considered to have a theoretical energy density of about 240 mAh/g.
However, since the metal fluorides represented by the general formula MF3 are electrically insulating, the electromotive force of non-aqueous electrolyte secondary batteries using the metal fluoride as a cathode active material is reduced during recharging and discharging in a high-current range. Such reduction disadvantageously makes it difficult for the batteries to generate high-capacity energy.